I called back and got the standard "not in service" message. Definitely spam. Maybe spoofed.
I don't know how voip calls work but since they seem to be assigned random phone numbers on CID, could that be one way this (not in service) can happen? I mean, there must be a pool of unassigned numbers for voip callers to call from. Could that be what is happening (rather than the spammer systematically spoofing a random phone number)?
Received call from this number, didn't answer, don't recognize the number although it is somewhat local. Caller ID screen came up, so I rejected it and blocked it. Caller ID, worth every penny these days.